I have a 1979 CJ 7 that had a stock 304 in it and I put in a 401. I took all of the smog off of it. The original fuel filter had a return line on it back to the fuel tank. Does anyone know why or what it was used for. I capped it off and put a regular filter on it. The engine has seemed like it is starving for gas after i run it hard even though I put an electric Fuel pump on in it. It could have something to do with a gas tank venting issue. Has anyone had similar problems or no a cure? Thanks.

Same set up here, with a 360. No pollution stuff, regular fuel filter, no return line.
Mine runs like a top. The only difference I can think of is I didn't cap the return line.
I just cut it off where the charcoal cannister used to be, and left it open.

The gas tank will vacuum lock with no vent and starve the engine for fuel.

The vent is the charcoal canister. That is a good thing to have working because it also ties with the PCV line. The PCV controls engine sludge and won't operate right without the added air flow from the canister.

Just the other day I went through this vapor lock issue with the fuel filter. If you are using the dual output filter w/return line, be sure it is installed correctly. It must be horizontal with the return line on the top. Otherwise, it will not return the vapors to the tank. Mine was installed incorrectly, and the return line was kinked. Although, I don't think I have a charcoal canister in the return path.